You are getting sleepy ... Wait, no, you aren't

You could say it’s a nightclub hypnotist’s nightmare. He calls a willing victim up to the stage, asks him to stare at the pocket watch, and then informs the audience member that he’s now a chicken.

But instead of clucking, or doing that arm flap thing, the smart-alecky subject winks at the audience and refuses to cooperate. But why are some people tough to hypnotize, while others seem to fall under the spell lickety-split?

David Spiegel, a physician in the department of psychiatry and behavioral sciences at Stanford University, and a team of colleagues, think they’ve discovered an important difference between people who are easy to hypnotize and those who aren’t.

According to the team’s study of 24 individuals, presented in the Archives of General Psychiatry, people with a low barrier to hypnosis have more functional connectivity between two areas of the brain: the left dorsolateral prefrontal cortex -- a region vital for executive functions – and the “salience network” – parts of the brain including the anterior cingulated cortex, amygdala, ventral striatum – that assigns importance to emotional, autonomic and somatic information.

In other words, parts of the brain that are constantly on the lookout for signals, and attaching emotional meaning to the input, and part of our prefrontal cortex that develops “action plans” about how to react to such signals, are communicating with each other more powerfully.

Spiegel used an example to explain what this means in real life. For example, a high hypnotizable person might sit down in the university library stacks to study, and lose all track of time because he’s so absorbed in the work. Or, when watching a movies, a high hypnotizable person might become so absorbed in it, he forgets it’s even a movie.

“It’s that when you are tracking something, you’re not worried about tracking something else,” Spiegel explained.

To figure this out, the researchers used 24 adults, mainly Stanford students, who, using a standard test called the Hypnotic Induction Profile, scored as either high or low hypnotizability.

Both groups were examined in a functional magnetic imaging (fMRI) machine. They were given no specific instructions regarding what to think about while in the machine, a “resting state.” There were no differences in physical brain structure or in the volume of various brain regions.

But there was a difference in function: The brains of people who were “high hypnotizable” showed that the dorsolateral prefrontal cortex was being functionally incorporated into the “salience network.” This didn’t happen in the low hypnotizable group.

“Normally, the dorsolateral prefrontal cortex is thinking, planning, deciding what to do next. And the anterior cingulate cortex is telling you what to be worried about,” Spiegel said. “In high hypnotizable people, these two tend to be functionally connected.”

The fact there wasn’t any difference in brain structure leads Spiegel to suggest that brain signaling chemicals might be responsible for the difference. People have different gene variants, called polymorphisms, that carry instructions for the way dopamine works in the brain. Previous studies have found that some polymorphisms are correlated with hypnotizability, cognitive function, alertness. So Spiegel thinks that’s a likely candidate to explain the difference in function between the two groups.

The study has its limitations, Spiegel admitted, like the low number of subjects, and the fact they weren’t hypnotized while in the fMRI. But the work is important, he said, because hypnosis is now often used for pain relief, to dampen anxiety in cancer patients undergoing treatment, and in psychotherapy. Knowing who’s likely to benefit could go a long way to making it an even more valuable tool.